A custom positron emission tomography (PET) scanner has been designed and built to provide characteristics tailored to the specific needs of NINCDS. During this year the full 7 slice capability has been implemented and the scanner has been in routine usage in conjunction with about a dozen clinical protocols. In addition, considerable effort has been applied to performance evaluation and to the suppression of several minor artifacts. This work will continue during the coming year, with particular emphasis on refinements of the spatial sampling program, interpolation, scatter correction, and elimination of ring artifact. It is also expected that animal studies at unusually high activity levels will be initiated, which will call for further study of several problems associated with very high count rates.